Document feeder and image reader

ABSTRACT

A document feeder comprises a hopper table on which documents are to be mounted, a feeding roller for transporting the documents mounted on the hopper table, and lifting system for raising and lowering the hopper table to position the topmost sheet of the documents mounted on the hopper table at a level of the feeding roller. The lifting system includes a hopper motor, and a drive mechanism for raising and lowering the hopper table by means of the driving force. The drive mechanism swings the hopper table when the hopper table is located between an lower limit position and a switching position above the lower limit position, or moves the hopper table vertically with maintaining its posture horizontally when the hopper table is located between the switching position and an upper limit position above the switching position. In addition, the height and the slant angle of the feeding roller sequentially conform to the movement of the hopper table in order to prevent jamming.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a document feeder for feeding adocument, and an image reader in which such a document feeder isprovided.

2. Related Arts

Recently, image readers have come to be widely employed for readingimages from documents. For many of these image readers, document feedersare provided for automatically feeding documents to the image readers.

To efficiently read a document, some image readers that are mainly forprofessional use employ document feeders which can mount a great number(e.g., several hundred or a thousand sheets) of documents at one time onhopper tables.

Generally, a document feeder is required to satisfy the followingconditions.

First, a feeding angle at which a document is fed to a feeding roller inan image reader (the same angle as the angle of a hopper table) must notexceed a permissible range for an ideal angle, regardless of the numberof documents remaining on the hopper table. This is because if thespread of the feeding angle exceeds the permissible range, paper feedingerrors, such as the jamming of documents or that a plurality of sheetsare fed at one time, may occur.

Second, the external dimension of the document feeder is small enough tosave an installation space.

Third, a power required for raising and lowering a document (on a hoppertable) is as small as possible in order to save the electric powerconsumption and to reduce the size of a drive source.

Conventional document feeders can generally be classified into twotypes: a parallel lift type and a swing type. In the parallel lift typedocument feeder, documents are stacked flat in a box-shaped orframe-shaped magazine and are raised and lowered with the magazine inthe horizontal state by the action of lifting means, so that the topmostsheet of the documents is fed to the level of a feeding roller.

This structure, however, has the following drawback. A distributed loadimposed by the documents affects the magazine. When a large number ofdocuments are mounted, such a distributed load is considerable.

For the parallel lift feeder, two reactive forces that support two endsof the documents against the distributed load must be coped with by thepower of the drive source. Further, not only the document but also themagazine must be raised or lowered. Therefore, a drive source that cangenerate a considerably great power is required. As a result, the sizeof the document feeder is increased, and a drive source having a largecapacity is required, so that the consumption of electric power isincreased.

In the swing type document feeder, an end of the hopper table ispivotally mounted on a specific shaft (i.e., is supported rotatablybetween a convex portion and a concave portion), so that the hoppertable can be swung around the rod in accordance with the number ofdocuments mounted on the hopper table.

With this structure, even when a large number of documents are mountedon the hopper table, among the reactive forces related to thedistributed load imposed by the documents, the reactive force on theshaft side is coped with by the static reactive force encountered at therod, and no load is placed on a drive source. Therefore, the requiredpower of the drive source is smaller than that of the parallel liftfeeder, and then this is preferable.

However, in order to restrict the angle of the hopper table for thisstructure within the permissible range, the length of the hopper table(the radius measured from the shaft) must be extended, so that the sizeof the document feeder is increased. If the length of the hopper tableis reduced, the angle through which the hopper table swings must beenlarged so as to handle a large number of documents. As a result, theswing angle of the hopper will exceed the permissible range. Therefore,paper feed errors will occur frequently, and then the image readingefficiency will be drastically reduced.

SUMMARY OF THE INVENTION

It is, therefore, one object of the present invention to provide adocument feeder that is compactly made and that can limit the occurrenceof paper feed errors, as well as an image reader that employs such adocument feeder.

To achieve the object, according to the present invention, provided is adocument feeder comprising:

a hopper table on which documents are to be mounted;

paper feeding means having a feeding roller which roller is so supportedthat the feeding roller contacts a topmost sheet of the documentsmounted on the hopper table and feeds the topmost sheet, and that aswing angle of said feeding roller relative to a horizontal plane ischangeable;

lifting means for raising and lowering the hopper table and forpositioning the topmost sheet of the documents at a level of the paperfeeding means; and

adjustment means for adjusting the swing angle of the feeding roller,

wherein the lifting means includes a drive source for generating adriving force, and a drive mechanism for raising and lowering the hoppertable by means of the driving force from the drive source; and

wherein the drive mechanism swings the hopper table when the hoppertable is located between a lower limit position and a switching positionset above the lower position, and moves the hopper table vertically withmaintaining its posture horizontally when the hopper table is locatedbetween the switching position and an upper limit position set above theswitching position; and

wherein the adjustment means makes the swing angle of the feeding rollercoincide with a slant angle of the hopper table when the hopper table islocated between the lower limit position and the switching position, andmaintains the feeding roller at a specific position when the hoppertable is located between the switching position and the upper limitposition.

Furthermore, according to another aspect of the present invention,provided is a document feeder comprising:

a hopper table on which documents are to be mounted;

transportation means for transporting the documents mounted on thehopper table; and

lifting means for raising and lowering the hopper table for positioninga topmost sheet of the documents mounted on the hopper table at a levelof the transportation means, the lifting means including a drive sourcefor generating a driving force and a drive mechanism for raising andlowering the hopper table by means of the driving force of the drivesource, the drive mechanism swinging the hopper table when the hoppertable is located between a lower limit position and a switching positionabove the lower limit position, or moving the hopper table verticallywith maintaining its posture horizontally when the hopper table islocated between the switching position and an upper limit position abovethe switching position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an image reader according to oneembodiment of the present invention;

FIG. 2 is a top view of a drive mechanism according to the embodiment ofthe present invention;

FIG. 3 is a side view of the drive mechanism according to the embodimentof the present invention;

FIG. 4 is a diagram for explaining an operation performed by adjustmentmeans according to the embodiment of the present invention;

FIG. 5 is a diagram for explaining the operation performed by theadjustment means according to the embodiment of the present invention;

FIG. 6 is a diagram for explaining the operation performed by theadjustment means according to the embodiment of the present invention;and

FIG. 7 is a flowchart for a control of a document feeder according tothe embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An image reader according to the preferred embodiment of the presentinvention will now be described while referring to the accompanyingdrawings.

First, an image reader incorporating therein the document feederaccording to one embodiment will be explained while referring to FIG. 1.Adjustment means, which will be described later, is omitted from FIGS. 1to 3 to avoid making the drawings overly complicated.

As shown in FIG. 1, a document feeder A is provided for the imagereader. The document feeder A has a hopper table 1 on which 1 to 1000documents 2 can be mounted. The hopper table 1 is raised and lowered bylifting means that includes a hopper motor 3 as a drive source, and adrive mechanism described later.

When the maximum number of documents 2 is mounted on the hopper table 1,it is located at a lower limit position S1 indicated by the solid line,in which the hopper table 1 is so inclined that a front edge 1a thereofis directed downward and a rear edge 1b is directed upward. The hoppertable 1 is swung upward from the lower limit position S1, and is leveledat a switching position S2 indicated by broken lines. Then, the hoppertable 1 is lifted horizontally from the switching position S2 to anupper limit position S3 indicated by chained lines.

The hopper table 1 is moved vertically so that the topmost document 2 isalways at a specified level (the level at which it contacts a feedingroller 4). As the individual sheets of the documents 2 on the hoppertable 1 are sequentially fed and the number of documents 2 is reduced,the hopper table 1 is gradually lifted from the lower limit position S1to the switching position S2, and from the switching position S2 to theupper limit position S3.

A lower limit position sensor 5 detects whether or not the hopper table1 is located at the lower limit position S1, and a switching positionsensor 6 detects whether or not the hopper table 1 is located at theswitching position S2. A hopper height sensor 7 emits a light directedat a part of the hopper table 1 where no documents 2 are stacked, andemploys reflected light to ascertain the height of the hopper table 1.

A feeding roller 4 that serves as paper feeding means rotates in thedirection indicated by arrow N1, and feeds the topmost sheet of thedocuments 2 in the direction indicated by arrow M. A detector 8 ispivoted around a shaft 9, in the vicinity of the feeding roller 4. Alower end 8a of the detector 8 is adapted to contact the topmost sheetof the documents 2, and a document sensor 10 detects an upper end 8b ofthe detector 8.

If there is even one document sheet 2 on the hopper table 1, thedocument 2 contacts the lower end 8a and the detector 8 is pivotedaround the shaft 9. Thus, the upper end 8b of the detector 8 is notdetected by the document sensor 10. In other words, when the upper end8b of the detector 8 is not detected by the document sensor 10, it isjudged that there is at least one document 2 on the hopper table 1.

When there are no documents 2 on the hopper table 1, since the detector8 does not swing at all, the document senor 10 detects the upper end 8bof the detector 8. That is, the document sensor 120 detects the upperend 8b of the detector 8 to determine whether there are no documents 2on the hopper table 1. The swing angle and the position of the feedingroller 4 are determined by adjustment means which will be describedlater.

The image reader is described hereinunder.

A separation roller 12, which rotates forward in the feeding direction Mof the documents 2, and a retarder roller 11, which rotates in thereverse direction, are provided directly adjacent to the feeding roller4 in FIG. 1, and in addition, conveyer rollers 14, 15 and 16 areprovided in the feeding direction M. The separation roller 12 and theretarder roller 11 are rotated by a feeding motor 13, and the conveyerrollers 14, 15 and 16 are rotated by a conveyer motor 17.

The obverse surface of the document 2 that is transported in the feedingdirection M is read by a first reader 18, and the reverse surface isread by a second reader 19. Image signals from the readers 18 and 19 aredigitized by a reading controller 20. The feeding motor 13 and theconveyer motor 17 are driven by a motor controller 21. The abovedescribed components are controlled by a main controller 22 thatincludes a CPU and a RAM, and the digital image data from the readingcontroller 20 are processed by the main controller 22.

A drive mechanism for the hopper table 1 will now be explained whilereferring to FIGS. 2 and 3.

As shown in FIG. 2, the document feeder in this embodiment comprises afixed chassis 30 and a sub-chassis 31 that is integrally formed with thechassis 30.

A hopper motor 3, such as a pulse motor, is fixed to the sub-chassis 31,and an output shaft 32 of the hopper motor 3 is linked with a series ofgears 33, which is fixed to a drive shaft 33a that is rotatably mountedin the sub-chassis 31 through a bearing. The rotational force of theoutput shaft 32 is transmitted via the series of gears 33 to a pinion 35that rotates vertically.

The chassis 30, the sub-chassis 31 and the drive mechanism downstreamfrom the gears 33 are also provided on the other side of the hoppertable 1, and the driving force is transmitted by the drive shaft 33a.The pinion 35 is pivotally mounted on a shaft 34 and is rotatablerelative to the sub-chassis 31.

As shown in FIG. 3, one end of a first link 37, which is positioned neara rear edge 1b of the hopper table 1, is pivotally mounted on a firstfixed support 36 provided in the chassis 30 in FIG. 2. The other end ofthe first link, which is positioned near a front edge 1a, is pivotallymounted to the hopper table 1 through a first shaft 38 at the side ofthe front edge 1a thereof.

The drive mechanism has a second link 40 crossing the first link 37. Oneend of the second link 40, which is positioned near the front edge 1a ofthe hopper table 1, is pivotally mounted on a second fixed support 39provided in the chassis 30. The other end of the second link 40, whichis positioned near the rear edge 1b of the hopper table 1, is pivotallymounted to the hopper table 1 through a second shaft 41 at the side ofthe rear edge 1b thereof.

An elongate protrusion 45 is provided in the middle of the first link37, and an arc-shaped elongate hole 46, with the first support 36serving as the center of the arc, is formed in the protrusion 45. Abottom end of the hole 46 serves as a pin seat 47. A connection pin 44is provided at the middle of the second link 40 to protrude into andslidably engage with the hole 46. An arc-shaped rack 42, with the firstsupport 36 serving as the center of the arc, is secured to the side ofthe first link 37 by screws 43 and engages the pinion 35.

The operation of the drive mechanism will now be explained whilereferring to FIG. 3.

When a large number of documents 2 are mounted on the hopper table 1, asis indicated by the solid lines in FIG. 3, the hopper table 1 is locatedat the lower limit position S1. The upper end of the rack 42 engages thepinion 35, and the connection pin 44 is located at the top end of theelongate hole 46. A slant angle θ of the hopper table 1 falls within apermissible range α.

As the number of documents 2 is reduced by the feeding of sheets, thepinion 35 rotates and the rack 42 is slowly turned. Accordingly, thehopper table 1 swings through the swing area T1 between the lowerposition S1 and the switching position S2. During this process, theconnection pin 44 does not move, while the elongate hole 46 moves upwardrelative to the connection pin 44. Thus, the second link 40 remains atthe position indicated by the solid line, and the driving force receivedat the pinion 35 is transmitted only to the first link 37, thereby thehopper table 1 merely swings around the first support 36.

When the hopper table 1 reaches the switching position S2, which isindicated by the broken line, the posture of the hopper table 1 is thenhorizontal. The elongate hole 46 slides upward relative to theconnection pin 44, which in turn contacts the pin seat 47 of theelongate hole 46. With this contact, the second link 40 is coupled withthe first link 37, and thus the links 37 and 40 cooperate with eachother to constitute the parallel linking mechanism. Therefor, thedriving force from the pinion 35 is transmitted not only the first link37 but also to the second link 40.

As a result, when the number of documents 2 is further reduced and thehopper table 1 is raised within a horizontal movement area T2 betweenthe switching position S2 and the upper limit position S3, thehorizontal posture of the hopper table 1 is maintained. In the horizonalmovement area T2, the hopper table 1 can be raised horizontally.

As described above, in the document feeder according to this embodimentof the present invention, a single linking mechanism serves to swing thehopper table 1 as well as to move it vertically with retaining itshorizontal posture. Therefore, an appropriate paper feeding can beperformed by a compact mechanism and a small driving force, withoutincreasing the slant angle and the length of the hopper table 1.

The adjustment means will now be described while referring to FIGS. 4, 5and 6. As shown in FIG. 4, the separation roller 12 rotates around animmobile shaft 50, and the left end of a feeding roller frame 51 ispivoted around the shaft 50 so that it swings in the direction indicatedby arrow N2. The feeding roller 4 is rotatably borne at the right end ofthe feeding roller frame 51. A suspension dog 52 is so fixed to thefeeding roller frame 51 that a lower end 52a of the dog 52 is positionedat the axis of the feeding roller 4.

At the rear of the first link 37 in FIG. 4, a sensor link 53 is providedfor rotating around a fixed support point 54. An elongate hole 55 isformed in the right end of the sensor link 53, and a pin 56 thatprojects from the side of the first link 37 is loosely inserted into theelongate hole 55, while a pin 57 is projected from the side of the leftend of the sensor link 53.

A vertical sensor plate 58 is positioned further to the rear of thesensor link 53 in FIG. 4. The sensor plate 58 is constantly pulleddownward by a spring 59. Longitudinal elongate holes 60 and 61 areformed in the sensor plate 58, and slidably receive fixed stoppers 62and 63, respectively. Guided by these elongate holes 60 and 61 and thestoppers 62 and 63, the sensor plate 58 can move vertically within aspecified range. In addition, a longitudinal elongate hole 64 is formedin the sensor plate 58 below the elongate hole 61, and a pin 57 slidablyengages with the elongate hole 64.

A dog sensor 65, which is a light transmission sensor, is provided onthe upper portion of the sensor plate 58 so that it projects toward therear of the sheet in FIG. 4. The dog sensor 65 detects the lower end 52aof the dog 52. When the hopper table 1 on which are mounted thedocuments 2 is raised from the lower limit position S1, the topmostdocument 2 contacts the feeding roller 4. When the hopper table 1 islifted further, the feeding roller 4 is pushed up and the feeding rollerframe 51 and the dog 52 are also turned upward. The hopper table 1(e.g., the first link 37) is controlled to rise until the lower end 52aturns off the dog sensor 65 (until a boundary of the ON/OFF switching).

When the hopper table 1 is located at the lower limit position S1,because there is a large number of documents 2, the hopper table 1, thesensor link 53, the sensor plate 58 and the feeding roller frame 51 arepositioned as shown in FIG. 4. That is, although the sensor plate 58 isalways pulled downward by the spring 59, the pin 57 is in contact withthe upper end of the extended hole 64, and then the sensor plate 58 cannot descend any further. The stoppers 62 and 63 are located in themiddle of the elongate holes 60 and 61, and do not restrict the movementof the sensor plate 58. In this situation, the swing angle (θ₁) of thefeeding roller frame 51 (the same as the inclination of the documents 2)and the slant angle (θ₂) of the face of the hopper table 1 on which thedocuments 2 are mounted are adapted to coincide with each other (θ₁=θ₂).

When the paper feeding is initiated and the topmost document 2 is fedinto the device, the feeding roller 4 descends a distance that isequivalent to the thickness of the document 2, and the swing angle ofthe feeding roller frame 51 is reduced (θ₁ →θ₁ '). At the same time, thedog 52 descends to turn on the dog sensor 65. Upon the detection ofthis, the hopper motor 3 is driven to raise the hopper table 1. When theslant angle θ of the first link 37 is reduced as the hopper table 1 islifted, the pin 56 is slightly elevated at the support 54, and the pin57 is lowered slightly. Accordingly, the dog sensor 65 (the sensor plate58) is lowered slightly and moved to a position where the swing angle(θ₁ ') of the feeding roller frame 51 coincides with the slant angle (θ₂') of the hopper table 1.

As shown in FIG. 5, when the hopper table 1 reaches the switchingposition S2, the first link 37 acts as a part of the parallel linkingmechanism, and the hopper table 1 is lifted with remaining its posturehorizontally.

In connection with the adjustment means, apparent from the comparisonbetween FIG. 4 with FIG. 5, the upper ends of the holes 60 and 61 aregradually lowered to contact the stoppers 62 and 63, respectively andthen the descent of the sensor plate 58 is inhibited. The swing angle(θ₁) of the feeding roller frame 51 is zero, and the feeding roller 4rotates at the same level as does the separation roller 12, therebyfeeding the document 2.

As the document feeding is continued and the hopper table 1 approachesnear the upper limit position S3, the positional relationship shown inFIG. 6 is obtained. That is, while the sensor plate 58 is maintained ata specific position because its descent is inhibited, the pin 57 ismoved downward from the position in FIG. 5 as the first link 37 isswung. However, since in the state shown in FIG. 5 the pin 57 contactsthe upper end of the longitudinal elongate hole 64 and a space forfurther movement of the pin 57 is ensured, the support 54 and the firstlink 57 can be swung with no trouble.

As described above, according to the adjustment means in thisembodiment, even when the hopper table 1 carries out a swing motion anda level lift motion sequentially by means of a drive mechanism, thefeeding roller 4 can smoothly follow the movement of the hopper table 1and can constantly maintain the appropriate posture for the hoppertable 1. Thus, feeding errors, such as paper jamming, can be prevented.

As described above, in this embodiment, the adjustment means isconstructed by employing a mechanical structure, but another structuremay be employed. For example, an encoder may be used to measure theslant angle of the first link 37, and based on the measured angle, anelectronic operation is performed to adjust the swing angle of thefeeding roller 4.

The operation of the document feeder according to this embodiment willnow be described while referring to FIG. 7.

The document feeder in this embodiment can handle a large number (about1000 sheets) of documents 2, as described above. However, a large numberof documents 2 is not always mounted on the hopper table 1, and in somecase, only a small number of documents 2 may be positioned on the hoppertable 1. When, as shown by the solid line in FIG. 3, the hopper table 1is always moved from the lower limit position S1, regardless of thenumber of documents 2, time is wasted before the topmost document 2reaches a predetermined level.

In this embodiment, the raising start height of the hopper table 1 isset to Hx, so that not only the lower limit position S1 but also theswitching position S2 can be selected. Thus, the saving in the time forraising the hopper table 1 is realized and the work efficiency can beincreased.

In FIG. 7, first, the above described lifting start height Hx isdetermined and the hopper table 1 is set at this height (step 1). Themain controller 22 outputs command signals to the motor controller 21 soas to drive the hopper motor 3, thereby raising the hopper table 1 (Step2). The main controller 22 checks the output of the document sensor 10to determine whether or not there is any document 2 on the hopper table1 (Step 3). If the document 2 is present, it is confirmed in a Step 4whether or not the topmost document 2 is flush with the feeding roller4. If "Yes", the process proceeds to a Step 5. If "No", the process backto the Step 2. The hopper table 1 is further raised until the topmostdocument 2 reaches the same level of the feeding roller 4, namely, untilthe lower end 52a of the dog 52 turns off the dog sensor 65.

The main controller 22 dose not need to monitor the hopper table 1 todetermine whether it is currently in the area T1 or in the area T2. Thisis because the drive mechanism can move the hopper table 1 appropriatelywithout any assistance of the main controller 22.

When the topmost document 2 reaches the level of the feeding roller 4,the movement of the hopper table 1 is stopped. The main controller 22outputs command signals to the reading controller 20 and the motorcontroller 21, respectively so as to drive the readers 18 and 19, andthe feeding motor 13 and the conveyer motor 17. Accordingly, thedocuments 2 fed from the feeding roller 4 are conveyed one by one in theconveying direction M by means of a set of the separation roller 12 andthe retarder roller 11, and the readers 18 and 19 read the obverse andreverse surfaces of the document 2 (Step 6).

The above described processes are repeated until there is no document onthe hopper table 1 (Steps 5-10). If no documents 2 is detected (Steps 3and 7), the process proceeds to a Step 11 in which the documentfeeding/reading is stopped. The main controller 22 outputs commandsignals to the reading controller 20 and the motor controller 21,respectively so as to make the readers 18 and 19 inoperative, and tostop the feeding motor 13 and the conveyer motor 17. Subsequently, themain controller 22 further outputs command signals to the motorcontroller 21 to drive the hopper motor 3, thereby moving down thehopper table 1 to the start height Hx (Step 12).

According to the present invention, since the swinging motion of thehopper table is changed into the horizontal raising motion of the hoppertable without discontinuity, even when a large number of documents ismounted on the hopper table, a driving force required for moving thehopper table and a required hopper table size are small, so that thedevice can be made compactly. In addition, when the slant angle and theheight of the hopper table are sequentially changed, an adequatepositional relationship for the feeding roller can be maintained, andthe occurrence of feeding errors can be limited.

What is claimed is:
 1. A document feeder comprising:a hopper table onwhich documents are to be mounted; paper feeding means comprising afeeding roller for contacting and feeding a topmost sheet of saiddocuments mounted on said hopper table; lifting means for raising andlowering said hopper table and for positioning said topmost sheet ofsaid documents at a level of said paper feeding means; and adjustmentmeans for adjusting a swing angle of said feeding roller, relative to ahorizontal plane, wherein said lifting means includes a drive source forgenerating a driving force, and a drive mechanism for raising andlowering said hopper table by means of said driving force of said drivesource; and wherein said drive mechanism swings said hopper table at avariable slant angle relative to said horizontal plane when said hoppertable is located between a lower limit position and a switching positionset above said lower position, and said drive mechanism moves saidhopper table vertically while maintaining its posture horizontally whensaid hopper table is located between said switching position and anupper limit position set above said switching position; and wherein saidadjustment means makes said swing angle of said feeding roller coincidewith said slant angle of said hopper table when said hopper table islocated between said lower limit position and said switching position,and maintains said feeding roller at a given position when said hoppertable is located between said switching position and said upper limitposition.
 2. An image reader comprising:a document feeder according toclaim 1; conveyer rollers for conveying a document from said documentfeeder; and a reading portion for reading said document from saidconveyer rollers.
 3. An image reader according to claim 2, wherein saidreading portion includes a first reader for reading an obverse surfaceof the document and a second reader for reading a reverse surface ofsaid document.
 4. A document feeder comprising:a hopper table on whichdocuments are to be mounted; transportation means for transporting saiddocuments mounted on said hopper table; and lifting means for raisingand lowering said hopper table for positioning a topmost sheet of saiddocuments mounted on said hopper table at a level of said transportationmeans, said lifting means including a drive source for generating adriving force and a drive mechanism for raising and lowering said hoppertable by means of said driving force from said drive source, said drivemechanism swinging said hopper table at a variable slant angle relativeto a horizontal plane when said hopper table is located between a lowerlimit position and a switching position above said lower limit position,and moving said hopper table vertically while maintaining its posturehorizontally when said hopper table is located between said switchingposition and an upper limit position above said switching position.
 5. Adocument feeder according to claim 4, wherein said drive mechanismincludes:a first link, one end of which, disposed at a rear end side ofsaid hopper table, is pivotally supported by a first fixed support andthe other end of which is supported by a first shaft on a front end sideof said hopper table, and to which link said driving force istransmitted from said drive source as a force for swinging said firstlink around said first support; and a second link, one end of which,disposed at the front end side of said hopper table, is pivotallysupported by a second fixed support and the other end of which issupported by said second shaft on the rear end of said hopper table,wherein a connection pin that projects from said second link slidablyengages a longitudinal elongate hole formed in the middle of said firstlink; wherein, when said hopper table is located between said lowerlimit position and said switching position, said connection pin slidesalong said elongate hole and only said swinging force of said first linkis transmitted to said hopper table; and wherein, when said hopper tableis located between said switching position and said upper limitposition, said connection pin contacts a pin seat at the bottom of saidelongate hole, so that said first link and said second link constitute aparallel linking mechanism to transmit, to said hopper table, saidswinging force of said first link as a horizontal raising/loweringforce.
 6. An image reader comprising:a document feeder according toclaim 4; conveyer rollers for conveying a document from said documentfeeder; and a reading portion for reading the document from saidconveyer rollers.
 7. An image reader according to claim 6, wherein saidreading portion includes a first reader for reading an obverse surfaceof the document and a second reader for reading the reverse surface ofsaid document.
 8. An image reader comprising:a document feeder accordingto claim 5; conveyer rollers for conveying a document from said documentfeeder; and a reading portion for reading the document from saidconveyer rollers.